The purpose of the present work is to establish the function of IgD on murine B lymphocytes. This will be done by determining: 1. The relationship between the epitope density of the antigen, the requirements for IgD vs IgM on the cell and the need for T cell help. 2. The relationship between the acquisition of IgD and the ability of the B cell to respond to antigens in vitro. 3. The ability of anti-delta vs. anti-mu to trigger B cells in the absence or presence of nonspecific T cell help.